Refractory fired shaped element and process of its manufacture

ABSTRACT

Novel refractory-fired, shaped elements for closures in pouring units for steel, iron and metal (nozzles, stoppers, spouts, slides) are provided. Said elements are based on zirconium oxide and zirconium silicate. The elements have advantageous thermal and mechanical properties and are economical to produce. A novel process for the production of these elements is also provided.

United States Patent 1 Schwarz [451 Aug. 12,1975

[ REFRACTORY FIRED SHAPED ELEMENT AND PROCESS OF ITS MANUFACTURE [75] lnventor: Hans Georg Schwarz, Marktredwitz,

211 Appl. No.; 45am;

[30] Foreign Application Priority Data Apr. 30, 1973 Germany 2321810 [52] US. Cl, 106/57 [51] Int. Cl. C04B 35/48 [58] Field of Search 106/57 [56] References Cited UNITED STATES PATENTS 2,553,265 5/1951 Mochel 106/57 2,593,352 4/1952 Shaw et al. 106/57 2,624,097 l/1953 Kistler 106/57 3,175,919 3/1965 Smoot et a1 106/57 3,228,778 1/1966 Walther et al. 106/57 3,620,781 11/1971 Garvie 106/57 Primary Examiner-J. Poer Attorney, Agent, or F irm-Wenderoth, Lind & Ponack [5 7 ABSTRACT Novel refractory-fired, shaped elements for closures in pouring units for steel, iron and metal (nozzles, stoppers, spouts, slides) are provided. Said elements are based on zirconium oxide and zirconium silicate. The elements have advantageous thermal and mechanical properties and are economical to produce. A novel process for the production of these elements is also provided.

6 Claims, No Drawings 1 REFRACTORY FIRED SHAPED ELEMENT AND PROCESS OF ITS MANUFACTURE 60 by weight of the entire amount of zirconium oxide present must be in stabilized form and 70 4O Refractory closures are employed in connection with pouring the molten steel from ladles. Such closures are situated in or on the pouring unitsThe task of such refractory closures is to maintain, as constant as possible, the amount of steel flowing out therethrough per unit of time, in order to optimize the. subsequent solidification and cooling process. The amountof steel flowing out per unit of time is substantially a function of the level of the steel bath i'n'the casting'unit and of the cross section of the opening of the closure.

Accordingly, the closures are subjected torigorous requirements in regard to the resistance to wear, in relation to the steel, iron or metal flowing the rethrough high temperatures, and particularly in regard; to resistance to deterioration as a result steep changes of temperatures, since the pouring units providedwith the ties of employing nozzles of zirconium silicate are limited. The difficulties associated with zirconium silicate nozzles result during long casting periods and while casting rimmed or alloyed steels. The severe stress manifests itself in the noticeable widening of the cross section of the nozzle opening, which leads to an uncontrolled variation in the rate of pour. Previous attempts to remedy this problem included employment of closures made of zirconium oxide or dense aluminum oxide. However, wide application of such products is prevented by the price of the material, which is very high in comparison with the products of zirconium silicate, and, most importantly, by a high sensitivity to thermal shock, which is found in such products.

Experiments employing mixtures of zirconium oxide and zirconium silicate as starting material for refractory bricks have also been made. Thus, Harders- Kienow, in their book, Feuerfestkunde, pages 9067 1960), Springer-Verlag proposed to employ a mixture of 1000 g zirconium oxide and 500 g zirconium silicate (66.66 by weight ZrO and 33.34 by weight ZrSiO,) for making light refractory bricks. However, the employed brick is employed only for the purpose of insulation. Due to its high porosity, it cannot be employed as shaped element for closures of casting units which transmit the flow of fused steel. On the contrary, a shaped element for pouring purposes must be dense in order to resist effectively the corrosion.

The invention is based on the task of developing a reasonably priced, quality zirconium-based material for shaped elements to be inserted into closures in casting units for steel, iron and metal, which encompasses the advantages of a high resistance to wear and to a high resistance in regard to thermal shocks.

The problem is solved by employing a composition comprising zirconium oxide at 10 50 by weight, preferably 35 by weight, zirconium silicate at 50 9O by weight, preferably 65 by weight. Moreover,

by weight must be in a non-stabilized form. The zirconium oxide is employed in a grain size of at most 0.1 mm, and preferably smaller than 0.06 mm, and the zirconium silicate is introduced in a grain size exceeding 02 mm, preferably 0.2 O.5 mm.

The portion of zirconium oxide (grain size under 0.1 mm, preferably smaller than 0.06 mm) is based on the idea of introducing this valuable material only in an amount required for a good resistance to corrosion. In the completed brick, this corrosion-resistant material forms the matrix, due to its fine grains, which matrix is resistant to slag corrosion.

The employment of inexpensive zirconium silicate in H -material, which'is more succep tibleto slag corrosion 20'" then zirconium oxide, is'made si'rnilar to that of zirconium oxide through its employment in theform of coarse grains (0.2 0.5 mm).

silicate comprising an intermediate matrix of sintered ""zirc onium oxide. Since the known dissociation of the ZrSiO, at high temperatures zrsio, zro SiO proceeds from the inner surface, the fractionof silicic acid released through decomposition in the composition of the mixtureof the invention (ZrSiO, being in coarser grain) is smaller by a multiple than the fraction corresponding to the quantitative substitution of the ZrSiO in the mixture by ZrO This again leads to the fact that the matrix contains a smaller amount of lowmelting compounds and, consequently, is much more effective against the corrosive action at high temperature. Moreover, the ZrSiO framework confers a good stability in relation to the variation of temperature to the fired product.

The zirconium oxide to be added in accordance with the invention is a material that in its original modification, exhibits reversible changes of volume at increased temperature (above 1000C), which leads to cracks in the structure of a mass which contains this material in excess. This disadvantage is avoided by employing stabilized zirconium oxide. In order to avoid the introduction of fluxing materials into the matrix of zirconium oxide beyond a certain extent and the resulting detrimental effect exerted on its refractory properties, the addition of stabilized zirconium oxide, containing CaO as stabilizer (as is well known), is quantitatively limited.

The upper limit of the additive is situated at about 60 by weight of the entire zirconium-oxide material. On the other hand, there is required a minimum amount, in order to obtain the stabilizing effect in the mixture (minimum amount: 30 by weight of the amount of zirconium oxide).

The shaped elements are manufactured both in accordance with the ceramic slurry casting process and also in accordance with the pressing process. ln order to avoid contamination of the starting material, a zirconium-oxide-containing slurry is used in the casting process. In the pressing process, this slurry or organic binding materials are employed as binders. In order to avoid contamination of the zirconium material through abrasion of foreign substances, the slurry is produced in a wet mill whose lining consists of shaped elements of zirconium oxide, which elements in suitable shape also perform the function of grinding elements.

The invention is explained on the following exemplified embodiments:

a. Slurry-casting process A mixture of 83 kg. stabilized zirconium oxide, grain size less than 0.1 mm, and 83 kg. nonstabilized zirconium oxide, grain size less than 0.1 mm, with 34 liters water and 5 ml. aqueous solution of an alkali salt of a polycarboxylic acid, is ground for 200 hours in a wet mill charged with grinding elements of zirconium oxide, and provided with a lining of zirconium oxide bricks. After 200 hours, 60 parts by weight of zirconium silicate, grain size 0.2 0.5 mm, is added to 40 parts by weight of such a slurry and a mixture is made. The mixture is cast into gypsum molds, removed after 12 hours, dried and fired at 1620C.

b. Pressing process In a muller mixer, there are mixed 650 kg. zirconium silicate, grain size 0.2 0.5 mm, while adding 15 liter sulfite waste liquor (30B), with 175 kg. stabilized zirconium oxide, grain size smaller than 0.06 mm, and 175 kg. nonstabilized zirconium oxide, for about 10 minutes. The completed mass is pressed on a hydraulic press under 500 kg./cm pressure. The pressed blank is dried and then fired at 1620C.

The steel-pouring nozzles produced in accordance with this process possess the following properties:

Chemical analysis: ZrO- '71 by weight CaO 1.5 by weight SiO, 20 by weight Physical Properties: Gross density 4.0 g/cc Specific gravity (weight) 5.0 g/cc Total porosity 20 by volume When employed in steelworks, the nozzles of the invention withstood the tests of use with excellent results.

1 claim: I

l. A refractory fired shaped element for closures in casting units for metals, said element comprising 10 to 50 by weight zirconium oxide and 50 to by weight zirconium silicate, 30 to 60 by weight of the total amount of zirconium oxide being present in stabilized form and 70 to 40 by weight of the total amount of zirconium oxide being present in unstabilized form.

2. A refractory fired shaped element as in claim 1, characterized in that the zirconium oxide is employed in a grain size smaller than 0.1 mm.

3. A refractory fired shaped element as in claim 1, characterized in that the zirconium silicate is introduced in a grain size larger than 0.2 mm.

4. A refractory fired shaped element as claimed in claim 1 wherein the total stabilized and unstabilized zirconium oxide is present at about 35% by weight and the zirconium silicate is present at about 65% by weight.

5. A refractory fired shaped element as claimed in claim 1 wherein the zirconium oxide grain size is smaller than about-0.06 mm.

6. A refractory fired shaped element as claimed in claim 1 wherein the zirconium silicate grain size is about 0.2 0.5 mm. 

1. A REFRACTORY FIRED SHAPED ELEMENT FOR CLOSURES IN CASTING UNITS FOR METALS, SAID ELEMENT COMPRISING 10 TO 50% BY WEIGHT ZIRCONIUM OXIDE AND 50 TO 90% BY WEIGHT ZIRCONIUM SILICATE, 30 TO 60% BY WEIGHT OF THE TOTAL AMOUNT OF ZIRCONIUM OXIDE BEING PRESENT IN STABILIZED FROM 70 TO 40% BY WEIGHT OF THE TOTAL AMOUNT OF ZIRCONIUM OXIDE BEING PRESENT IN UNSTABILIZED FORM.
 2. A refractory fired shaped element as in claim 1, characterized in that the zirconium oxide is employed in a grain size smaller than 0.1 mm.
 3. A refractory fired shaped element as in claim 1, characterized in that the zirconium silicate is introduced in a grain size larger than 0.2 mm.
 4. A refractory fired shaped element as claimed in claim 1 wherein the total stabilized and unstabilized zirconium oxide is present at about 35% by weight and the zirconium silicate is present at about 65% by weight.
 5. A refractory fired shaped element as claimed in claim 1 wherein the zirconium oxide grain size is smaller than about 0.06 mm.
 6. A refractory fired shaped element as claimed in claim 1 wherein the zirconium silicate grain size is about 0.2 -0.5 mm. 